1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to an electrochemical cell dischargeable under both an constant discharge rate and a pulse discharge rate. Cardiac defibrillators present both electrical power requirements.
The constant discharge rate portion of the multiplate cell of the present invention, referred to hereinafter as the medium rate region, preferably includes a high mass, low surface area cathode structure associated with an alkali metal anode in a side-by-side prismatic configuration. The pulse discharge rate portion of the multiplate cell of the present invention, referred to hereinafter as the high rate region, preferably includes a high surface area cathode associated with an alkali metal anode in a side-by-side prismatic configuration. Preferably the same anode structure is electrically associated with both the medium rate cathode region and the high rate cathode region housed within the same hermetically sealed casing. This structure defines what is meant by a medium rate region and a high rate region contained within the same electrochemical cell.
2. Prior Art
Traditionally, cardiac defibrillator cells have been built using a multiplate electrode design. The cell designer must decide between providing additional electrochemically active components for increased mass and energy density or providing increased surface area for greater power density. Because of the wide disparity in the energy/power requirements placed upon a cardiac defibrillator cell or battery, that being intermittent low rate and high rate operation, a compromise is often decided upon. However, any design attempt to balance the energy/power requirements placed upon the cell or battery by the defibrillator device must not consequently produce unwanted self-discharge reactions. This compromise can provide for inefficiency and can decrease the overall gravimetric and volumetric energy density of the cell.
It is generally accepted that when low electrical currents are desired, the electrodes within a cell should have as much mass and as little surface area as possible. At the expense of power density, this provides for increased energy density while the low electrode surface area minimizes undesirable self-discharge reactions. Conversely, when larger electrical discharge currents are required, electrode surface area and power density are maximized at the expense of energy density and self-discharge rate.
The cell of the present invention having an electrode assembly with differing discharge rate portions fulfills this need. The present cell comprises regions containing a low interelectrode surface area in a side-by-side, prismatic configuration, preferred for routine monitoring by a device, for example a cardiac defibrillator, and regions containing a high interelectrode surface area in a side-by-side, prismatic configuration for use when high rate electrical pulse charging of capacitors is required with minimal polarization. It is believed that the present electrochemical cell having multiplate electrodes with differing discharge rate regions represents a pioneering advancement wherein a medium discharge rate region and a high discharge rate region are provided within the same case for the purpose of having the cell supply at least two different electrical energy requirements.